This application relates to feeding of sheet material, and particularly to apparatus for separating sheets which are intentionally or inadvertently superimposed upon one another. Known apparatus for separating such sheet material may be found in U.S. Pat. No. 3,831,928.
As shown by the aforesaid patent, it is known to separate superimposed sheets of a sheet stack by feeding the sheet stack into the nip between a conveyor belt with a high coefficient of friction with respect to the sheet material and a friction member. The friction member engages the edge of the stack of sheets, and the coefficient of friction between the friction member and the sheet material is less than that between the conveyor and the sheet material, as well as being higher than the coefficient of friction between the sheets of the stack, so that only the bottom sheet is fed forward.
The friction member is mounted for movement towards and away from the surface of the conveyor and is urged toward engagement with the sheet conveyor. Such types of sheet separating apparatus as satisfactory in the cases where sheets having substantially uniform thickness across their width enter the nip between the friction member and the conveyor with their leading edges substantially parallel to the front edge of the friction member. In fact, however, especially where documents are being fed to a copier for example, a sheet so entering a separator may not always be of uniform thickness across its width since sheets may be dog-eared and have doubled portions or the like. Nor will the sheet always enter the nip between the conveyor and the friction member with its leading edge exactly parallel to the front edge of the friction member.
An additional drawback to known sheet feeding and separating apparatus is that in providing for the necessary degree of frictional engagement between the friction member and the sheet material it has been necessary to bias the friction member in such a manner that when no sheet is passing thereunder the friction member is urged into contact with the moving conveyor belt. This means that as the sheet material is separated and the last sheet passes the fricttion member the friction member is in frictional engagement with the conveyor belt. In practice, it has been found that this tends to place a highly undesirable retarding load on the mechanism which drives the conveyor, and to subject the conveyor belts to possible chattering and erratic feeding motion, and the friction member as well as the belts to undue wear.